1. Field of the Invention
This invention pertains to steelmaking converters, and in particular to a rotary converter having a vessel which is not only tiltable on trunnions but also rotatable about its own axis at right angles with the trunnion axis. The invention relates also to methods of making steel by using the converter and to methods of applying refractory linings to the inner surface of the converter.
2. Description of the Prior Art
Among well-known steel converters are the top-blown pure-oxygen converter, the bottom- and side-blown converters, the Kaldo converter, and the rotor converter. Of these the top-blown pure-oxygen converter, known also as the Linnz and Donnewitz (L-D) converter or the basic oxygen furnace (BOF) converter, has won perhaps the most extensive acceptance among steelmakers the world over. This greater popularity of the L-D or BOF converter comes from its lower installation cost, higher productivity, and superior quality of the steel produced.
The L-D converter has its own drawbacks, however. One of these is the rapid consumption of the refractory lining, although this is a problem common to all steelmaking furnaces. Another is its low desulfurizing are dephosphorizing capabilities. Intensive efforts are under way in various quarters to overcome these problems, and two measures have already been suggested to make up for refractory consumption.
The first is the spraying of powdered refractories. The second calls for a refining operation with the use of a high magnesia-content slag, formed by addition of lightburned or raw dolomite or the like, and the subsequent coating of that slag on the worn refractory lining. These and similar conventional measures are subject to the following objections.
1. The converter vessel may become untiltable because of undue slag accumulation on its bottom refractory.
2. The steel shell of the vessel may be overheated, and so deformed or even molten, owing to the uneven wear of the refractory lining, especially at the side of the vessel, and to its improper repair.
3. The refractory lining may strip off the shell under the weight of the slag adhering thereto.
4. Excessive slag attachment to the vessel lining may decrease the actual vessel capacity, resulting in increased slopping.
5. Excessive slag attachment to the bottom lining of the vessel may affect the level of the bath.
6. The converter must be operated with utmost care against the danger accruing from the above five possible causes, either individually or in combinations of two or more.
7. Steel production may decrease by reason of extended downtime due to frequent repairs of the refractory lining.
8. Skilled repairmen, required to work under excessive heat, must be on a full-time service.
9. No substantial saving is realized in the amounts of the refractory materials used, including those necessary for repairs such as lightburned or raw dolomite and powdered refractories.
Thus, while the conventional measures have certainly achieved a remarkable extension of the life of refractory linings, they can hardly be acclaimed as fundamental remedies for refractory consumption because of the above enumerated objections.
Some problems encountered in the practice of the conventional refractory repair measures will not be considered. These known measures work well for refractory consumption in certain localized regions of the vessel lining. The foregoing objections arise because the high magnesia-content slag cannot possibly be coated, or the powdered refractories cannot be efficiently sprayed, on the other lining regions.
The obvious reason for this is that the vessel can be tilted 360 degrees only about the axis of the trunnions at right angles with the vessel axis. Since the vessel is substantially cylindrical in shape, and since the vessel is tilted in one and the same plane, the molten metal and slag therein contact only the limited areas of the refractory lining. Only such limited lining areas can therefore be repaired by the conventional slag-coating method, inviting uneven consumption of the lining. The powdered refractories cannot also be effectively sprayed on some lining areas of particular angular dispositions.
The only practical solution to these difficulties is to make the vessel rotatable about its own axis, besides being tiltable about the trunnion axis. Two rotary converters have already been suggested and used, namely, the Kaldo converter and the rotor converter. Both of these known rotary converters rotate about inclined, nearly horizontal axes to afford the intermixing of molten metal and slag with a view to better desulfurization and dephosphorization. The construction of the Kaldo converter (shown in FIGS. 1 and 2 of the accompanying drawings) will be later explained in some detail, and its structural problems pointed out.
What follows is a list of engineering factors that merit due consideration in designing and constructing such rotary converters.
1. The total weight of the vessel and associated parts to be revolved in as much as from several hundred to more than 1000 tons.
2. The vessel and its support structures are subjected to temperatures ranging from room temperature to 400.degree. C. and, in some instances, as high as 700.degree. C. or more.
3. The direction of the load which the vessel exerts on the trunnion ring varies 360.degree. about the trunnion axis.
4. The entire converter equipment must operate properly under the most severe conditions, with exposure to high-temperature molten slag, combustion gases, metal splashes, and iron oxide dust.
5. Utmost constructional and operational safety is required since the converters are to handle molten metal at temperatures well over 1,600.degree. C.
In addition to all these considerations, rotary converters, if they are to gain true practical utility, should be simple, rugged, and maintenance-free in construction and compact in size.